Abstract 2317: Prostanoid EP4 receptor induces cleavage of HSP90 via ROS generation in human colon cancer cells

Abstract

Abstract Prostaglandin E2 (PGE2) has been reported to play critical roles in cell fate decision by interacting with four types of G protein-coupled membrane receptors such as EP1, EP2, EP3 and EP4. We previously reported that EP4 stimulation by treatment with its agonist CAY10598 induced apoptosis via reactive oxygen species (ROS) formation in colon cancer HCT116 cells. Moreover, treatment with CAY10598 diminished the phosphorylation of JAK2 and induced degradation of this oncoprotein, leading to the attenuation of STAT3 activation in HCT116 cells. In the present study, we attempted to delineate the molecular mechanisms underlying the degradation of JAK2 by activation of EP4. HSP90, a member of the heat shock protein family, is a molecular chaperone that supports stability of client proteins, such as, EGFR, MET, Akt and JAK2. HSP90-mediated stabilization/activation of these client proteins contributes to the acquisition of cancer cell hallmarks, including proliferation, survival, angiogenesis and invasion. It has been recently reported that the chaperoning function of HSP90 may be disrupted by post-translational modification induced by oxidative stress. Treatment of human colon cancer HCT116 cells with CAY10598 down-regulated expression of HSP90 client proteins in a concentration- and time-dependent manner and the down-regulation was restored by pretreatment with ROS scavenger N-acetyl cysteine (NAC) or proteasome inhibitor MG132. However, cotreatment with cycloheximide, protein synthesis inhibitor, accelerated the CAY10598-induced degradation of HSP90 client proteins. These data suggest that CAY10598-induced HSP90 client protein degradation may be caused by ROS generation. In renal carcinoma Caki cells, CAY10598 also down-regulated expression of HSP90 client proteins, suggesting that EP4 stimulation may regulate HSP90 activity in colon cancer cells as well as renal cancer cells. We found that HSP90α was cleaved to 40 or 55 kDa, while HSP90β cleaved to 25 kDa by CAY10598 treatment and the cleavage of HSP90α and β was blocked by NAC treatment. Furthermore, EP4 inhibition by treatment with antagonist GW627368x attenuated not only degradation of HSP90 client proteins but also cleavage of HSP90 in CAY105998-treated HCT116 cells. In conclusions, EP4 agonist CAY10598 induces degradation of HSP90 client proteins via ROS-dependent HSP90 cleavage, leading to apoptosis in HCT116 cells. This is a novel mechanism by which EP4 activation induces apoptosis of cancer cells that involved inhibiting HSP90 function. Citation Format: In Gyeong Chae, Mi-hee Yu, Kyung-Soo Chun. Prostanoid EP4 receptor induces cleavage of HSP90 via ROS generation in human colon cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2317. doi:10.1158/1538-7445.AM2017-2317